You know the saying "There's Always a Bigger Fish"? Well, it also applies to crime and criminals. When a story opens with a thief, kidnapper, or murderer "getting away with it" or proceeding with stage 3 of their 4 step plan, they may run into Colliding Criminal Conspiracies when they get entangled along with or caught in the traps of another, bigger or more professional criminal... or monster.
If they took some Innocent Bystanders for hostages, then both kidnapped and kidnappers are going to have to work together if they want to get out alive. Usually though, this threat is so grave they fast forward past Stockholm Syndrome and/or Lima Syndrome and develop true loyalty for each other that can last a lifetime. If they survive, that is.
This isn't to say all is forgiven and the criminals turn over a new leaf, and make them truly sympathetic by pitting them against a truly worse adversary. Quite the contrary, they might show that they're really rotten by showing that after their need for Teeth-Clenched Teamwork has passed, they plan to kill their former kidnap victims, and/or by using the hostages as Human Shields and dying thanks to their stupidity. Good riddance to that Asshole Victim. Interestingly, both of the above can exist in the same story if one criminal repents and the other doesn't.
Likely candidates for conspiracies to collide into are: Arriving at the home of Mad Scientist, Cannibal Tribe, or some sort of monster. One especially deliciously ironic variant is to unwittingly kidnap a monster. Due to the high stakes, expect the protagonists (both kidnapped and kidnappers) to have to choose between leaving the loot and living, or getting the gold and potentially dying. Compare Unintentionally Notorious Crime, which might overlap.
- Baccano! combines this with the odd case of Mugging the Monster, with everything from trainfulls of rival mobsters encountering a conductor who's an Ax-Crazy assassin with a twisted sense of justice (and a great deal of respect for the colleague they murdered to infiltrate the train) to immortals having their elixir of life stolen by random muggers.
- This is the big reveal in Bookhunter. Two different thieves, acting completely independently, plot to steal a valuable book. The first thief leaves a replica in the original's place, and the second thief steals the replica. It's only after solving the mystery of the second theft that the police realize that the first theft happened at all.
- In the The Flash storyline "Crossfire," the Rogues launch their long-planned takeover of Keystone City...only to have the Thinker choose the same time to launch his own attack on Central City and the battle of the two forces allows the Flash to defeat them both.
- When the The Punisher is held in a small town cell during the Suicide Run event, several criminal enterprises set out independently to get him, turning the town into a war zone.
- From Dusk Till Dawn: Two gunmen brothers kidnap a preacher and his children, only to take refuge in a brothel/strip joint infested with vampires.
- House on Haunted Hill:
- In House on Haunted Hill (1999) (the remake), the host and his wife are planning their own roundabout ways to kill each other during the party. Shame it should just happen that the house really is haunted, and filled with exceedingly sadistic and powerful ghosts.
- The original movie also plays with this trope as the host and his wife in this film are planning to kill each other as well. The host succeeds.
- The French movie The Nest has a great example of this. A big warehouse complex is being used as a hideout by some fairly mundane thieves, but ends up as the site for a huge battle between terrorists and a good-guy military squad.
- Psycho: A secretary runs off with several thousand dollars and holes up in the Bates Motel. Things end poorly for her.
- Splinter: A married couple are taken hostage by a couple of criminals. During a pit stop for gas, they're attacked by a horrible monster that takes over people as it devours them.
- In Whisper, a band of kidnapper discover the child they've abducted is very, very much not a normal little boy.
- In The Usual Suspects, a bunch of would-be robbers end up stealing from and in the pockets of a much more sinister crime lord. The only reason they were kept alive is because they didn't realize who they were stealing from at the time of robbery and they are forced to repay with another crime.
- The plot of Snatch. is driven by a variety of criminals vying over a diamond, intersecting with Irish Travelers clashing with an underground boxing promoter.
- Lock, Stock & Two Smoking Barrels is the intersection of four lowlifes trying to pay off a gambling debt, a group of thugs stealing from a black gang's pot growing operation, and a crimelord ordering the theft of some valuable muskets.
- Played with in Hard Rain where a fairly simple plotline about a bunch of criminals trying to rob an armoured truck becomes more complicated when the local law enforcement decide to steal the cash themselves and the van guard and the lead robber end up in an Enemy Mine.
- Worst case yet must be Deep Rising, where a Gambit Pileup has a thief, mercenaries, a captured cruise ship and a pack of sea monsters.
- Malevolence is about a group of bank robbers who accidentally wind up inside the house of a psychotic murderer.
- The Collector has a man who tries to rob a house's safe and encounters a serial killer who broke into the place before he did.
- Scarecrows features a robbery of the Camp Pendleton payroll which goes wrong when the robbers have to land in a field filled with evil scarecrows.
- Fatal Instinct: Both Ravine's unfaithful wife Lana and released convict Max Shady plot to kill him on the same train ride. Lana ends up shooting Shady by mistake because he also wears Ravine's trademark blue suit.
- Man on Fire had this as the cause of the main plot. The ransom drop off went horribly wrong because several groups got too greedy. Aside from the Voice and his gang (the actual kidnappers), a group of cops tried to steal the ransom money for themselves, as well as the victim's family lawyer stealing half the ransom as it was being transported. Creasy ends up unraveling the plots of each group as he hunts each of them down and kills them.
- They Re Playing With Fire starts off as a movie where a married couple plan to drive the husband's mother and grandmother away from their home mansion with a help from a high school student. Then a guy in a ski-mask starts killing people around the place.
- The Neighbor: A couple of drug runners discover that their neighbor runs a kidnapping-for-ransom operation next door.
- The film Flypaper has two robber gangs (a couple of Stupid Crooks and somewhat more competent commando-type thieves and it's eventually revealed that a famous cat burglar had been working on the inside for a while prior as a cashier) barging into a bank and taking the people inside hostage while they try to rob different parts of it (after a while of going through a Mexican Standoff and then declaring "This Is My Side, this is your side")... and then it turns out that they were both baited into robbing the bank on the same day by a criminal mastermind Chessmaster that wanted to use all of them as chaff for his own heist (and the murder of a Dirty Cop accomplice that had outlived his usefulness) and Kill 'em All afterwards.
- Lake Bodom: Four teenagers decide to go camping near lake Bodom, where murders took place in 1960. Two of them are plotting to kill the other half of the group and make them disappear but, unbeknownst to them, they are being stalked by a genuine psycho killer...
- Frontier(s): Bunch of French thieves exploit riots to perform a heist and then hide in a hotel on the French countryside... that is the home of a Cannibal Clan in the vein of The Texas Chainsaw Massacre.
- In Kim Newman's No Gold in the Grey Mountains, a band of thieves try to rob a coach of its gold. It doesn't have any (a Title Drop is deployed), so they opt for a hostage ploy on the little girl who's aboard instead. Back at their hideout, some ancient thing is stirred up, and begins picking them off one-by-one...
- The first Varg Veum story has a child abduction mixed with a murder and a plot to illegally sell hazardous chemicals. They all intersect in the worst possible way when it's revealed that the abductor couldn't possibly have known that he had the child.
- Happens at a bank robbery with almost immediate turnaround at the beginning of Steelheart.
- Happens a couple times with rival spy agencies on Alias. Most notable in the early seasons with Sark and his "flexible loyalties." Most of his plans started with big successes, only for him to get caught or entwined in another spy's scheme. He'd then switch sides or at least pretend to, evoking a very temporary truce. Even the finale showed that his tendency to let whoever's conspiracy he collided with take precedence allowed him to be the only Big Bad to survive.
- Person of Interest features two sets: the various power battles for control of New York's criminal underworld and the conflict over control of The Machine. From time to time, the two sets will intersect for an even bigger collision. The series ends with both of the crime dons that were part of the major cast buying the farm because they — evil or morally grey — didn't really had the understanding or firepower to deal with something as powerful as the Samaritan conspiracy when it decided to "purge" them.
- The Last Heist is about a Bank Robbery that takes place at the same time that a Serial Killer who likes to carve out and collect his victims' eyes happens to be in the building to retrieve his 'trophies' from the vault. It also turns into a Hostage Situation when the police catch on to the robbery taking place. And several corrupt SWAT team members are also after the loot.
- In The Gamer's Alliance, the Nightstalkers end up entangled in the complex rival plots of Matheson Crime Family, the Order of the Black Rose and the Totenkopf cult, all of which take place in Maar Sul City. The gang tries to make the most out of it in the dangerous environment but does suffer quite a bit along the way because they simply aren't powerful enough to upstage the other influential factions in their own game.
- Mega64 Version 3: The antagonistic organization Falz is afraid of a group of incredibly dangerous assassins they call The Killers. It shortly turns out that the Mega64 gang has had run-ins with members of The Killers before.
- Evil Con Carne: This trope was the reason Hector decided to start the League of Destruction.